The physical and chemical characteristics of natural and synthetic rubbers can be changed by hydrogenation. For instance, the tensile strength and resistance of a rubber to various solvents can often be improved by hydrogenating the rubber.
Numerous rubbers contain double bonds in their backbones as well as pendant vinyl groups. For example, in the synthesis of polybutadiene generally both 1,2-addition and 1,4-addition occurs with the polybutadiene consequently containing both 1,2- and 1,4-microstructures. The 1,4-addition causes the polybutadiene to have double bonds in its backbone and the 1,2-addition causes the polybutadiene to have pendant vinyl groups. The hydrogenation of such diene rubbers containing double bonds in their backbone as well as vinyl unsaturation with conventional hydrogenation catalysts normally result in a fast rate of vinyl hydrogenation relative to hydrogenation of the double bonds in the polymer's backbone. However, it would be highly desirable to selectively hydrogenate the double bonds in the backbone of elastomers. For example, the resistance of such polymers to ozonolysis is improved by selectively hydrogenating double bonds in the polymer's backbone with pendant vinyl groups, which can be utilized in curing or functionalizing the elastomer, being retained. Ozone attack on such vinyl groups will not cleave the polymer's backbone and will not appreciably lower the polymer's molecular weight or change its chemical or physical properties.